The Stem Cell and Pathology Core will be a critical resource to this PPG. It will provide the four Projects with access to a wide array of reagents, procedures, and analyses, including i) CPC isolation, sorting, and characterization, ii) assays of CPC function in vitro, and iii) histopathology of cardiac samples obtained in vivo. It will provide the facilities and expertise necessary to isolate, maintain, and manipulate CPCs from several genetically engineered mice. The individual Projects do not have the facilities or expertise needed to isolate and characterize CPCs consistently or to perform the extensive histopathological analyses required. Consolidation of all CPC work into a Core facilitv will decrease the costs of supplies and eguipment because the Core will make bulk purchases of supplies (thereby reducing expenses) and because waste and unnecessary duplication of supplies, reagents, and equipment will be eliminated with the maintenance of centralized stocks and inventories. Consolidating CPC work into a Core facilitv is also time-effective because the techniques involved in this work are very labor intensive and require dedicated, skilled personnel. The Core staff, a full-time team of six dedicated individuals under the immediate supervision of the Core Leaders, will provide consistency and reproducibility of analvsis. This is crucial, because it will ensure that all four Proiects will use CPCs isolated, expanded, and sorted the same way, thereby making the results comparable. A single source of CPCs with rigorous standardization to ensure consistency will result in transplantation of uniform CPC populations in all four Proiects and thus is extremely important for the integration and comparison of results from each of the Projects. Similarly, the uniform histopathologic analyses conducted by the Core in a blinded and rigorously standardized fashion will make it possible to compare results of different experiments within the same Project and among different Projects. The methods used by the Core to prepare CPCs are extremely efficient; CPCs in culture, as determined by c-kit expression (FACS). average 953% at passages 2 to 10 and remain at -95% at passage 10. In summary, the Core will ensure guality control and, by eliminating duplication of effort and maximizing the use of personnel and supplies, will enable an efficient use of resources.